Media captionUS Secretary of State Mike Pompeo says the Saudis will respond in a “timely fashion”

However, Saudi Arabia says reports on Mr Khashoggi’s death are “completely false and baseless” and that it is “open to co-operation” to find out what happened.

Several high-profile human rights groups have demanded that Turkey ask the UN to investigate the possible killing of Mr Khashoggi.

Amnesty International, Human Rights Watch, Reporters Without Borders and the Committee to Protect Journalists said that a “one-sided” investigation by Saudi Arabia was not good enough.

On Wednesday and Thursday, Turkish investigators spent almost nine hours searching the Saudi consul’s residence, before moving on to the consulate itself about 200m (650ft) away, according to Reuters news agency.

Several vehicles with Saudi diplomatic number plates were filmed by CCTV cameras moving from the consulate to the residence just under two hours after Mr Khashoggi entered the consulate.

Late on Thursday, Turkish officials told journalists police were searching Belgrad Forest – a secluded woodland more than 10km (six miles) from the capital Istanbul – as well as Yalova city nearby.

An official told Reuters they suspected that Mr Khashoggi’s remains had been disposed of in “a farm house or villa” in one of those areas.

Investigators had taken samples from the Saudi consulate and the consul’s home, and would analyse them for traces of Mr Khashoggi’s DNA, the official, who Reuters did not name, added.

How have other countries reacted?

Saudi Arabia is a key ally to many Western countries, especially the US. As one of the world’s biggest oil exporters, it has significant influence on the world stage.

The Dutch and French finance ministers, and the head of the International Monetary Fund, are amongst those now boycotting the summit.

He said there would be “very severe” consequences if Saudi Arabia was proved to have killed the journalist.

However, Mr Trump has also been accused of providing cover to the Saudi government.

He previously said he would not cancel military contracts with Saudi Arabia because “I don’t want to hurt jobs”, and also said he was unhappy Saudi Arabia was being treated as “guilty until proven innocent”.

Russian President Vladimir Putin has said it is a pity that Mr Khashoggi has gone missing, but that Russia cannot damage relations with Saudi Arabia without hard facts.

Image copyrightAFP/Getty Images

Image caption
Hatice Cengiz said she waited outside the consulate for 11 hours, but did not see her fiancé

Who is Jamal Khashoggi?

Mr Khashoggi is a prominent journalist who has covered major stories for various Saudi news organisations.

He served as an adviser to top Saudi officials, but later fell out of favour with the government.

He went into self-imposed exile in the US last year, and wrote a monthly column in the Washington Post.

The newspaper said the column had been submitted by Mr Khashoggi’s translator the day after he was reported missing.

It had initially held off from publishing the column, but decided to go ahead after accepting Mr Khashoggi was not going to return safely.

In his column, Mr Khashoggi criticised the state of press freedom in the Arab world, saying it left Saudis “either uninformed or misinformed”.

Government moves to suppress journalists “no longer carry the consequence of a backlash from the international community”, he wrote. “Instead, these actions may trigger condemnation quickly followed by silence.”

Jamal Khashoggi disappearance: The key events

2 October

03:28: A private jet carrying suspected Saudi agents arrives at Istanbul airport. A second joins it late afternoon

12:13: Several diplomatic vehicles are filmed arriving at the consulate, allegedly carrying some of the Saudi agents

13:14: Mr Khashoggi enters the building, where he is due to pick up paperwork ahead of his marriage

15:08: Vehicles leave the consulate and are filmed arriving at the nearby Saudi consul’s residence

21:00: Both jets leave Turkey by 21:00

3 October

Turkish government announces Mr Khashoggi is missing, thought to be in the consulate

4 October

Saudi Arabia says he left the embassy

7 October

Turkish officials tell the BBC they believed Mr Khashoggi was killed at the consulate. This is later strongly denied by Saudi Arabia